The present invention is related to a transmitter used in combination with a compact and portable CD player, and also to an automobile audio apparatus using such a transmitter.
Even when no CD player is installed, or mounted on an automobile, if an FM radio is installed, or mounted on this automobile, then music recorded on a CD can be reproduced by using the speakers connected to this FM radio while a portable CD player and, for example, a transmitter 20 as shown in FIG. 1 are employed and this FM radio is operated. In other words, in FIG. 1, reference numeral 10 indicates a portable CD player, i.e., the normal type portable CD player having the various sorts of operation keys 11, an LCD 16 for displaying thereon the operation conditions, a headphone jack 12, and an external power supply jack 15 to which a DC voltage derived from an AC adaptor is applied as an operation voltage.
It should be understood that in the normal portable type CD player 10, speakers are not built therein. When a user listens to music recorded on a CD by using only such a normal portable type CD player 10, the user connects a headphone to the headphone jack 12 so as to listen to the music via this headphone.
A transmitter 20 include an FM transmitter circuit (not shown) for converting a stereophonic audio signal into an FM signal produced in accordance with the specification of the presently available FM broadcasting system. Moreover, this transmitter 20 has a plug 21 insertable into a cigarette lighter socket of an automobile (not shown). A cord 23 whose tip portion is connected to the headphone plug 22 is conducted from this transmitter 20, and also a cord 24 whose tip portion is connected to the DC plug 25 is conducted from this transmitter 20.
Then, when a user listens to a CD by using the FM radio installed on the automobile, the user inserts the headphone plug 22 into the headphone jack 12, and further inserts the DC plug 25 to the power supply jack 15. In addition, the user inserts the plug 21 into the cigarette lighter socket of the automobile.
As a result, the DC voltage appearing at this cigarette lighter socket is derived from the plug 21, and then is applied as the operation voltage to the FM transmitter circuit built in the transmitter 20, so that this FM transmitter circuit is brought into the operative state.
In addition, the DC voltage derived from the plug 21 is applied via the cord 24 and the plug 25 to the jack 15, and will become the operation voltage for the CD player 10.
Then, the key 11 is manipulated to set the CD player 10 to a reproduction mode. As a result, the CD is reproduced by this CD player 10 to output the audio signal reproduced from this CD to the headphone jack 12. This audio signal is supplied via the plug 22 and the cord 23 to the FM transmitter circuit of the transmitter 20 so as to be converted into the FM signal. Thus, this FM signal is transmitted in the wireless signal from outside the transmitter 20. At this time, when a knob 26 is rotated, the transmission frequency of this FM signal may be changed, or adjusted.
As a consequence, when this transmitted FM signal is received by the FM radio installed in the automobile, the music recorded on the CD reproduced by the CD player 10 can be heard from the speakers installed in this automobile. At this time, all of the functions of the CD player 10 may be utilized by manipulating the key 11.
Furthermore, since the power supply voltage of the CD player 10 is derived from the cigarette lighter socket, no battery is required in this CD player 10. Also, the user need not pay attention to depletion of this cell energy.
As explained above, in accordance with this transmitter 20, the portable CD player 10 may be used in a similar manner to the CD player mounted on the automobile. This conventional technique is disclosed in, for example, U.S. Pat. No. 4,712,250.
In such a case that the user listens to the music recorded on the CD by using the above-explained transmitter 20, first, the user is required to set the reception frequency of the installed FM receiver to such a frequency of the FM broadcasting band where no broadcasting program is transmitted, namely an empty frequency. Next, the user must tune the transmission frequency of the transmitter 20 to the reception frequency of the FM receiver. Then, in order to perform this tuning operation, the user must rotate the knob 26 of the transmitter 20 so as to vary the transmission frequency while the user listens to the sounds produced from the speakers connected to the FM receiver.
However, such a tuning operation requires very cumbersome manipulations. In particular, very cumbersome and heavy workloads are necessarily required so as to seek the empty frequency in such a region where a large number of FM broadcasting programs are transmitted, for instance, in USA.